Internal combustion engine

ABSTRACT

An internal combustion engine in which component parts slide against each other during operation, the internal combustion engine including: a water supply device that supplies water to the sliding surfaces of the component parts; and a control device that controls an operation of the internal combustion engine. At least one of the sliding surfaces of the component parts is made of silicon-based ceramics. The control device controls the operation of the internal combustion engine such that a low load or a no-load operation in which an engine load is limited to a predetermined reference load or less is performed until a predetermined standby period elapses after the operation of the internal combustion engine is started, and controls the operation of the internal combustion engine such that a normal operation in which the engine load is not limited to the reference load or less is performed after the standby period elapses.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2022-079023 filed on May 12, 2022, incorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to an internal combustion engine.

2. Description of Related Art

Conventionally, there has been known an internal combustion engine in which sliding portions of a plurality of members in a combustion chamber are made of a ceramic material or a ceramic-coated material, and water is used for lubrication in the combustion chamber (Japanese Unexamined Patent Application Publication No. 6-159087 (JP 6-159087 A)). JP 6-159087 A states that the use of water for lubrication in this way makes it possible to clean the inside of a cylinder and suppress knocking by a cooling effect of the water.

Also, Yoshikazu Kimura, “Lubricating with Water”, Journal of the Japan Society of Mechanical Engineers, 2005.4, Vol. 108, No. 1037, p17 to p19, discloses that SiC forms a SiO₂ layer that is softer than a base material through a tribochemical reaction, suppresses solid contact between the base materials, and reacts with water to form a softer hydroxide or hydrate, which functions as a kind of lubricant to protect a surface and reduce friction.

SUMMARY

However, it has not always been possible to adequately lubricate mutually sliding component parts of an internal combustion engine by simply using a ceramic material for a sliding portion and supplying water to the sliding portion.

In view of the above problems, an object of the present disclosure is to enable more appropriate lubrication of mutually sliding component parts of an internal combustion engine.

The gist of the present disclosure is as follows.

(1) An internal combustion engine in which component parts slide against each other during operation, the internal combustion engine including:

-   a water supply device that supplies water to sliding surfaces of the     component parts; and -   a control device that controls an operation of the internal     combustion engine, -   in which at least one of the sliding surfaces of the component parts     is made of silicon-based ceramics, and -   in which the control device controls the operation of the internal     combustion engine such that a low load or a no-load operation in     which an engine load is limited to a predetermined reference load or     less is performed until a predetermined standby period elapses after     the operation of the internal combustion engine is started, and     controls the operation of the internal combustion engine such that a     normal operation in which the engine load is not limited to the     reference load or less is performed after the standby period     elapses.

The internal combustion engine according to (1), in which the standby period is a period required for a cumulative sliding distance between the sliding surfaces of the component parts to reach a predetermined fixed distance.

The internal combustion engine according to (2), in which the standby period is a predetermined fixed time.

The internal combustion engine according to (1), further including a concentration parameter detection device that detects a value of a concentration parameter that changes in accordance with a concentration of impurities contained in water supplied to the sliding surfaces, in which the water supply device repeatedly supplies water to the sliding surfaces, the water being water that has already been supplied to the sliding surfaces, and in which the standby period is a period until a change speed of the value of the concentration parameter detected by the concentration parameter detection device becomes equal to or less than a predetermined reference value.

The internal combustion engine according to (4), in which the concentration parameter is an electrical resistance of water supplied to the sliding surfaces.

The internal combustion engine according to (1), further comprising a resistance parameter detection device that detects a value of a resistance parameter that changes in accordance with a magnitude of a sliding resistance between the component parts,

in which the standby period is a period until the value of the resistance parameter detected by the resistance parameter detection device becomes a value indicating that the magnitude of the sliding resistance is equal to or less than a predetermined reference value.

The internal combustion engine according to (6), in which the internal combustion engine is configured to be driven by a motor, and

in which the resistance parameter is an output of the motor when the internal combustion engine is driven by the motor so as to reach a predetermined rotational speed.

The internal combustion engine according to any one of (1) to (7), in which the water supply device includes a filter that removes powder of the silicon-based ceramics contained in water supplied to the sliding surfaces.

The internal combustion engine according to any one of (1) to (8), further including a storage portion in which water after being supplied to the sliding surfaces is stored; and a stirring device that stirs water stored in the storage portion,

in which the water supply device supplies water stored in the storage portion to the sliding surfaces, and

in which the control device causes the stirring device to stir water stored in the storage portion until the standby period elapses after the operation of the internal combustion engine is started.

The internal combustion engine according to any one of (1) to (9), including a cylinder and a piston ring that is provided on an outer circumference of a piston that reciprocates within the cylinder, as the component parts that slide against each other.

The internal combustion engine according to (10), in which the water supply device includes a water jet for spraying water toward the piston and a piston passage provided in the piston, and

in which the piston passage is provided such that water sprayed from the water jet flows into the piston passage and water in the piston passage is supplied to the piston ring.

The internal combustion engine according to any one of (1) to (11), in which the internal combustion engine is an internal combustion engine that uses hydrogen as fuel.

According to the present disclosure, it is possible to more appropriately lubricate mutually sliding component parts of an internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

FIG. 1 is a schematic cross-sectional side view of an internal combustion engine;

FIG. 2 is a cross-sectional side view in which the vicinity of a cylinder of the internal combustion engine is enlarged;

FIG. 3 is a diagram schematically showing a hardware configuration of a vehicle regarding a control of the internal combustion engine;

FIG. 4 is a diagram showing a time transition of a load of the internal combustion engine when an operation of the internal combustion engine is started;

FIG. 5 is a flowchart showing a control routine for controlling the operation of the internal combustion engine;

FIG. 6 is a flowchart similar to FIG. 6 showing the control routine for controlling the operation of the internal combustion engine;

FIG. 7 is a flowchart similar to FIG. 5 showing the control routine for controlling the operation of the internal combustion engine;

FIG. 8 is a schematic cross-sectional side view of an internal combustion engine according to a fourth embodiment;

FIG. 9 is a schematic cross-sectional side view of an internal combustion engine according to a fifth embodiment;

FIG. 10 is a diagram schematically showing a hardware configuration of a vehicle regarding a control of the internal combustion engine according to the fifth embodiment; and

FIG. 11 is a flowchart similar to FIG. 5 showing the control routine for controlling the operation of the internal combustion engine 1.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference to the drawings. In the following description, similar component parts are given the same reference numbers.

First Embodiment Configuration of Internal Combustion Engine

First, the configuration of an internal combustion engine according to a first embodiment will be described with reference to FIGS. 1 to 3 . The internal combustion engine 1 according to this embodiment is a hydrogen engine in which hydrogen is supplied as fuel into a combustion chamber. Further, in this embodiment, the internal combustion engine 1 is mounted on a vehicle 100. The vehicle 100 is a hybrid electric vehicle having an electric motor for driving the vehicle 100 in addition to the internal combustion engine 1. In particular, in this embodiment, the internal combustion engine 1 is mainly used as a generator for generating electric power to be supplied to an electric motor, and the vehicle 100 is mainly driven by the electric motor.

FIG. 1 is a schematic cross-sectional side view of the internal combustion engine 1. FIG. 2 is a cross-sectional side view in which the vicinity of a cylinder of the internal combustion engine 1 is enlarged. In the following description, the upper side of FIGS. 1 and 2 is the upper side of the internal combustion engine 1 and the lower side of FIGS. 1 and 2 is the lower side of the internal combustion engine 1. However, for example, the up-down of FIGS. 1 and 2 do not necessarily match the up-down of the internal combustion engine 1.

As shown in FIGS. 1 and 2 , the internal combustion engine 1 has a cylinder block 2, a cylinder head 3, a piston 4, a crankcase 5, and a water pan 6. One or more cylinders are formed in the cylinder block 2, and the piston 4 reciprocates up and down within these cylinders. The cylinder head 3 is arranged on the cylinder block 2, and a combustion chamber 7 is defined by the cylinder head 3, the cylinder, and the piston 4.

The cylinder block 2 has a cylinder liner 11 defining the cylinder for each cylinder. The cylinder is thus formed by the inner surface of the cylinder liner 11. The cylinder liner 11 is made of silicon-based ceramics. Specifically, in this embodiment, the cylinder liner 11 is made of silicon carbide (SiC). The cylinder liner 11 may be made of other silicon-based ceramics such as silicon nitride (Si₃N₄). Accordingly, in this embodiment, the surfaces defining the cylinder are formed of silicon-based ceramics.

The cylinder block 2 itself may define each cylinder, without the cylinder block 2 having the cylinder liner 11. In this case, the cylinder block 2 is made of silicon-based ceramics. Alternatively, the surface of the cylinder liner 11 or cylinder block 2 that forms the cylinder may be coated with silicon-based ceramics. In any event, the surfaces defining the cylinder are formed of silicon-based ceramics.

The cylinder head 3 is arranged on the cylinder block 2 and closes the upper part of the cylinder formed in the cylinder block 2. The cylinder head 3 is provided with a spark plug 12 arranged in the center of the top surface of each combustion chamber 7 and a fuel injection valve 13 arranged in an outer peripheral region of each combustion chamber 7. The fuel injection valve 13 injects fuel into the combustion chamber 7 and the spark plug 12 ignites the air-fuel mixture formed in the combustion chamber 7.

In the cylinder head 3, an intake port 14 through which intake gas flows is formed, and an intake valve 15 for opening and closing the intake port 14 is provided. The opening and closing of the intake valve 15 is controlled by an intake variable valve mechanism capable of changing the valve opening and closing timing of the intake valve 15 and the lift amount of the intake valve 15. Further, the cylinder head 3 is formed with an exhaust port 16 through which exhaust gas flows, and is provided with an exhaust valve 17 for opening and closing the exhaust port 16. The opening and closing of the exhaust valve 17 is also controlled by an exhaust variable valve mechanism capable of changing the opening and closing timing of the exhaust valve 17 and the lift amount of the exhaust valve 17. Note that the intake variable valve mechanism and/or the exhaust variable valve does not need to be provided. In this case, in the intake valve 15 and/or the exhaust valve 17, the valve opening/closing timing and lift amount are kept constant.

The piston 4, as shown in FIG. 2 , has a plurality of grooves 21 on its outer periphery, each extending around the circumference. A piston ring 22 is arranged in each of these grooves 21. Each of the piston rings 22 is formed such that its outer surface is in contact with the inner surface of the cylinder liner 11. In this embodiment, the piston ring 22 is made of silicon-based ceramics. Specifically, the piston ring 22 is made of silicon carbide (SiC). The piston ring 22 may be made of other silicon-based ceramics such as silicon nitride (Si₃N₄). Also, a coating of silicon-based ceramics may be formed on the outer surface of the piston ring 22. Therefore, in this embodiment, both the outer surface of the piston ring 22 and the inner surface of the cylinder liner 11, which are sliding surfaces that slide against each other as the piston 4 reciprocates, are made of silicon-based ceramics.

Also, the piston 4 is connected to a crankshaft 24 via a connecting rod 23. The connecting rod 23 is connected to the piston 4 by a piston pin 25 and is connected to the crankshaft 24 by a crankpin 26 so as to convert the reciprocating motion of the piston 4 into the rotational motion of the crankshaft 24.

The crankcase 5 is arranged below the cylinder block 2 and fixed to the cylinder block 2. The crankcase 5 covers the crankshaft 24 so that the crankshaft 24 is not exposed to the outside.

The water pan 6 is arranged below the crankcase 5 and fixed to the crankcase 5. In this embodiment, water is used to lubricate the sliding surfaces of the component parts of the internal combustion engine 1. The water pan 6 functions as a storage section used to store the water used for lubrication in this way. The water used here may be just water, or may be water to which an additive or the like for rust prevention or antifreeze has been added.

Next, with reference to FIGS. 1 and 2 , the configuration of a water supply device for supplying water for lubricating the internal combustion engine 1 will be described. The water supply device supplies water stored in the water pan 6 to the sliding surfaces of the component parts of the internal combustion engine 1. In particular, in this embodiment, the water stored in the water pan 6 is supplied between the inner surface of the cylinder (the inner surface of the cylinder liner 11) and the outer surface of the piston ring 22.

As shown in FIGS. 1 and 2 , the water supply system includes a strainer 31, a pump 32, a water jet 33, and a piston passage 34 formed within the piston 4. When the pump 32 is driven, the water stored in the water pan 6 is sucked through the strainer 31 and sprayed from the water jet 33 (see arrow in FIG. 1 ). The water sprayed from the water jet 33 flows into the piston passage 34 formed in the piston 4 (see the arrow in FIG. 2 ), is supplied through the piston passage 34 into the groove 21 in which the piston ring 22 is provided, and is then supplied to the piston rings 22, in particular between the piston rings 22 and the cylinder liner 11.

The strainer 31 is a mesh filtering device for removing foreign matter mixed in the water stored in the water pan 6 and is arranged so as to be immersed in the water stored in the water pan 6. The strainer 31 communicates with the pump 32, and the water stored in the water pan 6 is supplied to the pump 32 through the strainer 31.

The pump 32 sucks up the water stored in the water pan 6 via the strainer 31 and supplies it to the water jet 33. The pump 32 is configured by, for example, an electric variable displacement pump. The pump 32 is connected to an engine ECU 40, which will be described later, and is controlled by a command from the engine ECU 40.

The water jet 33 is attached to the cylinder block 2 or the crankcase 5 below each cylinder. The water jet 33 sprays water supplied from the pump 32 toward the inside of the piston 4 and the wall surface of each cylinder.

A piston passage 34 formed in the piston 4 supplies the water sprayed toward the lower surface of the piston 4 by the water jet 33 to the groove 21 provided with the piston ring 22. The piston passage 34 includes an annular main passage (cooling channel) 34 a extending along a circumference of the inside of the piston 4, an inlet passage 34 b extending from the main passage 34 a to the lower surface of the piston 4, and an outlet passage 34 c communicating with each groove 21. The inlet passage 34 b is located on an extension line of the water jet 33 in the injection direction. Each outlet passage 34 c extends radially, and a plurality of outlet passages 34 c are provided between each groove 21 and the main passage 34 a. The outlet passages 34 c between each groove 21 and the main passage 34 a are provided at regular intervals in the circumferential direction.

In the piston passage 34 configured in this way, when water is sprayed from the water jet 33, the injected water flows into the inlet passage 34 b. The water that has flowed into the inlet passage 34 b flows in the main passage 34 a in the circumferential direction, and then flows into the groove 21 through the outlet passage 34 c.

Therefore, in this embodiment, part of the water sprayed from the water jet 33 is directly supplied onto the inner surface of the cylinder liner 11. A portion of the water sprayed from the water jet 33 is also supplied to the groove 21 through the piston passage 34. The water supplied to the inner surface of the cylinder liner 11 and the grooves 21 of the piston 4 in this way is then supplied between the outer surface of the piston ring 22 and the inner surface of the cylinder liner 11, that is, onto the sliding surfaces of the component parts of the internal combustion engine 1.

FIG. 3 is a diagram schematically showing a hardware configuration of the vehicle 100 regarding a control of the internal combustion engine 1. As shown in FIG. 3 , the internal combustion engine 1 has the engine ECU 40 that functions as a control device that controls the operation of the internal combustion engine 1. In addition, the internal combustion engine 1 has a concentration sensor 41 and an output sensor 42 as sensors for detecting various parameters related to the internal combustion engine 1. Further, the internal combustion engine 1 has a throttle valve 43 as an actuator used to control the internal combustion engine 1, in addition to the spark plug 12, the fuel injection valve 13 and the pump 32 described above. The vehicle 100 also includes a power control unit (PCU) 51 that controls the electric motor, and a motor ECU 50 that controls PCU 51. The PCU 51 includes, for example, an inverter and a DC/DC converter. The concentration sensor 41, the output sensor 42, the spark plug 12, the fuel injection valve 13, the pump 32, the throttle valve 43, the PCU 51, the engine ECU 40, and the motor ECU 50 are connected to each other via an in-vehicle network 63 conforming to standards such as a controller area network (CAN).

The concentration sensor 41 is a sensor that detects the concentration of impurities contained in the water stored in the water pan 6. The impurities include, for example, powder of silicon-based ceramics produced by scraping the sliding surfaces of the outer surface of the piston ring 22 and the inner surface of the cylinder liner 11 as they slide against each other. In particular, in this embodiment, the concentration sensor 41 detects the electric resistance of the water stored in the water pan 6 in order to detect the concentration of impurities. The higher the electrical resistance detected by the concentration sensor 41 is, the lower the concentration of impurities contained in the water stored in the water pan 6 is.

In this embodiment, the concentration sensor 41 detects the electrical resistance of the water stored in the water pan 6 as a concentration parameter that changes according to the impurity concentration. However, instead of the concentration sensor 41, a concentration parameter detection device that detects other concentration parameters that change according to the concentration of impurities contained in the water stored in the water pan 6 may be used. For example, the concentration parameter detection device may detect the transparency of the water stored in the water pan 6 in order to detect the concentration of impurities.

The output sensor 42 is a sensor that detects the output of the electric motor. The output sensor 42 detects the output of the electric motor, for example, based on the electric power supplied to the electric motor. In particular, when the internal combustion engine 1 is driven by the electric motor without fuel being supplied to the internal combustion engine 1, the output sensor 42 can detect the driving resistance of the internal combustion engine 1, that is, the frictional resistance between the component parts of the internal combustion engine 1.

The throttle valve 43 is provided in an intake passage of the internal combustion engine 1 and controls the flow rate of intake gas supplied to the combustion chamber 7. Therefore, the throttle valve 43 is used to control the operation of the internal combustion engine 1 together with the fuel injection valve 13 and the spark plug 12. In order to control the operation of the internal combustion engine 1, other devices such as a variable valve mechanism, an EGR valve, etc. may be further used.

The internal combustion engine 1 or the vehicle 100 may not have all the component parts described above. Therefore, the internal combustion engine 1 may not have the concentration sensor 41, the output sensor 42, or the like, for example.

Moreover, in the present embodiment, the internal combustion engine 1 is mainly used as a generator, but the internal combustion engine 1 may be used to directly drive the internal combustion engine 1 in addition to generating power. In this embodiment, the vehicle 100 equipped with the internal combustion engine 1 is a hybrid electric vehicle, but the vehicle 100 may be a vehicle that is driven only by the internal combustion engine 1 and that does not have an electric motor for driving the vehicle 100.

Lubrication by Water

As described above, in the internal combustion engine 1 according to this embodiment, the inner surface of the cylinder liner 11 and the outer surface of the piston ring 22 are made of SiC ceramics. Further, when the piston 4 reciprocates within the cylinder, that is, when the piston ring 22 slides on the cylinder liner 11, water is supplied to these sliding surfaces as described above.

Here, silicon-based ceramics such as SiC undergoes a chemical reaction represented by the following formula (1) due to a tribochemical reaction on the sliding surface when friction occurs in an environment where water is supplied, resulting in silicon dioxide SiO₂ being produced.

SiO₂ produced in this way is amorphous, soft, and has a low shear force. Therefore, when SiO₂ is generated on the sliding surface, the frictional resistance during sliding is reduced.

In addition, in an environment where water is supplied, SiO₂ is converted to a hydroxide (Si(OH)₄) or a hydrate (SiO₂·nH₂O) as shown by the following formula (2).

Si(OH)₄ and SiO₂·nH₂O thus produced function as a lubricant, thereby further reducing the frictional resistance during sliding.

Therefore, when the piston 4 reciprocates in the cylinder and the piston ring 22 slides against the cylinder liner 11 in an environment where water is supplied, SiO₂, Si(OH)₄, or SiO₂·nH₂O (hereinafter collectively referred to as “SiO₂ or the like”) is generated on the outer surface of the piston ring 22 and the inner surface of the cylinder liner 11, and the frictional resistance therebetween is reduced.

Such a phenomenon occurs not only in SiC ceramics but also in other silicon-based ceramics such as Si₃N₄. Therefore, even when the cylinder liner 11 and the piston ring 22 are made of silicon-based ceramics other than SiC, the friction reduction effect described above can be obtained.

Moreover, the phenomenon described above can occur when at least one of the sliding surfaces of the component parts that slide against each other is made of silicon-based ceramics. Therefore, as long as at least one sliding surface of the component parts that slide against each other is made of silicon-based ceramics, the other sliding surface may be made of another material. Therefore, when one sliding surface of the cylinder liner 11 and the piston ring 22 is made of silicon-based ceramics, the other sliding surface may be made of iron, aluminum, or the like.

Control When Starting

Almost no SiO₂ or the like remains on the inner surface of the cylinder liner 11 or the outer surface of the piston ring 22 while the internal combustion engine 1 is stopped. Therefore, when the operation of the internal combustion engine 1 is started (when the crankshaft 24 starts rotating from a stopped state), basically, almost no SiO₂ or the like remains on these sliding surfaces. Therefore, when the operation of the internal combustion engine 1 is started, the inner surface of the cylinder liner 11 and the outer surface of the piston ring 22 are likely to be damaged or worn due to the reciprocating motion of the piston 4 within the cylinder, and the friction loss easily becomes large. In particular, when the load of the internal combustion engine 1 is high and the pressure in the combustion chamber 7 is high, the pressing force of the piston ring 22 against the cylinder liner 11 is increased and the shake of the piston 4 due to vibration is increased and thus, scratches and wear especially tend to occur.

Therefore, in the present embodiment, the internal combustion engine 1 is controlled so that the low load operation is performed in which the load of the internal combustion engine 1 is controlled to a predetermined reference load or less until a predetermined standby period elapses after the operation of the internal combustion engine 1 is started. Thereafter, after the standby period has elapsed since the operation of the internal combustion engine 1 was started, the normal operation is performed in which the engine load is not limited to the reference load or less. Here, when the load of the internal combustion engine 1 becomes larger than the reference load, the reference load is a load in which large scratches and wear occur on the inner surface of the cylinder liner 11 and the outer surface of the piston ring 22 immediately after the internal combustion engine 1 starts operating. Moreover, although the upper limit load may be set during the normal operation of the internal combustion engine 1, the reference load is a load lower than the upper limit load.

FIG. 4 is a diagram showing a time transition of a load of the internal combustion engine 1 when an operation of the internal combustion engine 1 is started.

In the example shown in FIG. 4 , the operation of the internal combustion engine 1 is started (rotation of the crankshaft 24 is started) at time t1. When the operation of the internal combustion engine 1 is started at time t1, the internal combustion engine 1 is operated under a low load, and the load of the internal combustion engine 1 is set to a first load L1. The first load L1 is, for example, a minimum load required for the internal combustion engine 1 to operate, and is a load equal to or less than the reference load described above. The first load L1 is, for example, a load necessary for keeping the internal combustion engine 1 in an idling state. Therefore, after time t1, the engine ECU 40 operates various actuators (for example, the throttle valve 43, the fuel injection valve 13, the spark plug 12, etc.) of the internal combustion engine 1 so that the load of the internal combustion engine 1 becomes the first load L1.

When the load of the internal combustion engine 1 is set to the first load, it is maintained over the standby period. Here, the standby period is a period considered necessary for forming a film of SiO₂ or the like on the outer surface of the piston ring 22 or the inner surface of the cylinder liner 11 to a sufficient extent to suppress scratches and wear. Here, in order to form the film of SiO₂ or the like on the inner surface of the cylinder liner 11 and the outer surface of the piston ring 22, it is necessary for these sliding surfaces to slide a fixed distance. Therefore, in this embodiment, the standby period is the period required for these sliding surfaces to slide a fixed distance. In this embodiment, the standby period is set to a predetermined fixed reference time. It is considered that a sufficient film of SiO₂ or the like is formed on the outer surface of the piston ring 22 or the inner surface of the cylinder liner 11 after the standby period has passed. Therefore, when the standby period has passed, it is no longer necessary to perform the low load operation.

Therefore, in the present embodiment, as shown in FIG. 4 , the normal operation is performed in the internal combustion engine 1 after time t2 when the standby period has elapsed from time t1. The normal operation is the operation performed by the internal combustion engine 1 when the internal combustion engine 1 is not under special conditions such as the starting operation. In particular, in this embodiment, since the internal combustion engine 1 is used to generate electric power to be supplied to the electric motor, a fixed load is maintained during the normal operation so that the internal combustion engine 1 can be operated efficiently. Therefore, after time t2, the load of the internal combustion engine 1 is set to a second load L2. The second load L2 is, for example, a load that is set when the internal combustion engine 1 performs the normal operation, and is a load that is greater than the reference load described above. In particular, in this embodiment, the second load is set to a load that allows the internal combustion engine 1 to operate most efficiently. Therefore, after time t2, the engine ECU 40 controls various actuators of the internal combustion engine 1 so that the load on the internal combustion engine 1 becomes the second load L2.

FIG. 5 is a flowchart showing a control routine for controlling the operation of the internal combustion engine 1. The illustrated control routine is executed by the engine ECU 40 at fixed time intervals.

First, in step S11, the engine ECU 40 determines whether the time is after the operation of the internal combustion engine 1 has been started (step S11). When it is determined in step S11 that the time is not after the operation of the internal combustion engine 1 is started, that is, when the internal combustion engine 1 is stopped, the control routine is ended.

On the other hand, when it is determined in step S11 that the operation of the internal combustion engine 1 has started, the engine ECU 40 determines whether an elapsed time T from the start of operation of the internal combustion engine 1 is a predetermined reference time Tref (step S12). When it is determined in step S12 that the elapsed time T is less than the reference time Tref, the low load operation of the internal combustion engine 1 is performed, and the load of the internal combustion engine 1 is set to the first load L1 (step S13). On the other hand, when it is determined in step S12 that the elapsed time T is equal to or more than the reference time Tref, the normal operation of the internal combustion engine 1 is performed, and the load of the internal combustion engine 1 is set to the second load L2 (step S14).

Effects and Modifications

As described above, almost no SiO₂ or the like remains on the inner surface of the cylinder liner 11 or the outer surface of the piston ring 22 while the internal combustion engine 1 is stopped. Therefore, when the operation of the internal combustion engine 1 is started, these sliding surfaces are not lubricated sufficiently and thus, the sliding surfaces are likely to be damaged or worn.

On the other hand, in the present embodiment of the internal combustion engine 1, the low load operation is performed in the internal combustion engine 1 until the standby period elapses after the operation of the internal combustion engine 1 is started. Therefore, even when the operation of the internal combustion engine 1 is started, it is possible to suppress the sliding surfaces from being scratched or worn and thus, the component parts of the internal combustion engine 1 sliding with each other can be properly lubricated. A no-load operation in which there is no load may be performed in the internal combustion engine 1 until the standby period elapses after the operation of the internal combustion engine 1 is started. During the no-load operation, the internal combustion engine 1 is operated without fuel being supplied to internal combustion engine 1, and the internal combustion engine 1 is driven, for example, by an electric motor (or a starter motor).

Further, the internal combustion engine 1 according to this embodiment is a hydrogen engine in which hydrogen is supplied as fuel into the combustion chamber 7. Therefore, component parts such as CO₂ and SO_(x) are not contained in the exhaust gas accompanying fuel combustion. In this embodiment, since oil is not used as a lubricant, the exhaust gas discharged from the internal combustion engine 1 does not contain oil-derived CO₂, SO_(x), or the like. Therefore, according to the internal combustion engine 1 of the present embodiment, it is possible to keep the emissions of CO₂, SO_(x), and the like low. Since the lubrication of the component parts, which slide with each other, of the internal combustion engine 1 according to the present embodiment can be performed appropriately even in an internal combustion engine 1 that uses fossil fuel as fuel, the internal combustion engine 1 may be an internal combustion engine that uses fossil fuel as fuel.

In the above embodiment, the load of the internal combustion engine 1 is set to the fixed second load L2 larger than the first load L1 as normal operation. However, in the normal operation, operation may be performed in other manners, provided that the engine load is not limited. For example, when the vehicle 100 is driven by the internal combustion engine 1, the vehicle 100 may be driven with a load corresponding to the amount of depression of the accelerator pedal by the driver during the normal operation.

Further, in the above-described embodiment, the standby period during which the internal combustion engine 1 is operated under a low load is set to a fixed reference time. However, the standby period may be a period other than the fixed time as long as it is a period necessary for the sliding surfaces to slide a fixed distance. Therefore, the standby period may be, for example, a period from when the operation of the internal combustion engine 1 is started until the sliding surfaces slide a fixed distance, or after the operation of the internal combustion engine 1 is started until the cumulative number of revolutions of the crankshaft 24 reaches a fixed value. In any case, by setting the standby period based on the elapsed time from the start of the operation of the internal combustion engine 1, the sliding distance, or the cumulative number of rotations, it can be relatively accurately estimated that a film of SiO₂ and the like is generated without providing an additional sensor.

Furthermore, in the above-described embodiment, the sliding component parts of the internal combustion engine 1 are the cylinder liner 11 and the piston ring 22. However, component parts of the internal combustion engine 1 that slide against each other may be component parts other than the cylinder liner 11 and the piston ring 22 may be component parts such as the intake valve 15 and the intake cam that opens and closes the intake valve 15, or the exhaust valve 17 and the exhaust cam that opens and closes the exhaust valve. Also in this case, for example, the sliding surfaces of the intake valve 15 and the intake cam are made of SiC ceramics, and water is supplied to these sliding surfaces.

Second Embodiment

Next, the internal combustion engine 1 according to a second embodiment will be described with reference to FIG. 6 . The configurations of the internal combustion engine 1 and the vehicle 100 according to the second embodiment are basically the same as the configurations of the internal combustion engine 1 and the vehicle 100 according to the first embodiment. The following description will focus on the parts that are different from the internal combustion engine 1 and the vehicle 100 according to the first embodiment.

In the above-described first embodiment, the standby period was the period required for the sliding surfaces to slide a fixed distance. In contrast, in the second embodiment, the standby period is the period until a change speed of the concentration parameter that changes in accordance with the concentration of impurities contained in the water stored in the water pan 6, that is, the water supplied to the sliding surface becomes equal to or less than a predetermined reference value.

Here, in the present embodiment, the water supplied onto the inner surface of the cylinder liner 11 and the outer surface of the piston ring 22, that is, the sliding surfaces, is returned into the water pan 6. The water in the water pan 6 is supplied to the sliding surface via the pump 32 and the water jet 33. Therefore, in the present embodiment, the water that has been supplied to the sliding surface is repeatedly supplied to the sliding surface.

When a film of SiO₂ and the like is formed on the sliding surface, the sliding surface is sufficiently lubricated and thus, the sliding surface is hardly worn. On the other hand, when a film of SiO₂ and the like is not formed on the sliding surface, the sliding surface will not be sufficiently lubricated and thus, the sliding surface will wear. When the sliding surface wears in this way, the amount of powder such as SiC contained in the water stored in the water pan 6 increases. That is, the concentration of impurities contained in the water stored in the water pan 6 increases. Therefore, it is considered that a film of SiO₂ and the like is not formed on the sliding surface when the concentration of impurities is changing, and conversely, it is considered that a film of SiO₂ and the like is formed on the sliding surface when the concentration of impurities is not changing. Therefore, in the present embodiment, it is determined that a film of SiO₂ and the like is not formed on the sliding surface when the rate of change in the impurity concentration is faster than a predetermined reference rate, and it is determined that a film of SiO₂ and the like is formed on the sliding surface when the rate of change in the impurity concentration is equal to or less than the predetermined reference rate. This makes it possible to accurately detect the formation of a film of SiO₂ and the like on the sliding surface.

FIG. 6 is a flowchart similar to FIG. 5 showing the control routine for controlling the operation of the internal combustion engine 1. The illustrated control routine is executed by the engine ECU 40 at fixed time intervals. Steps S21, S23, and S24 in FIG. 6 are the same as steps S11, S13, and S14 in FIG. 5 , respectively, so description thereof will be omitted.

When it is determined in step S21 that the operation of the internal combustion engine 1 has started, the engine ECU 40 determines whether a change rate R of an electrical resistance detected by the concentration sensor 41 is equal to or less than a predetermined reference value Rref (step S22). The reference value Rref at this time is, for example, a value corresponding to the reference speed described above.

When it is determined in step S22 that the change rate R of the electrical resistance is faster than the reference value Rref, that is, when it is determined that the change rate of the impurity concentration is faster than the reference speed, the low load operation is performed in the internal combustion engine 1 (step S23). On the other hand, when it is determined in step S22 that the change rate R of the electrical resistance is equal to or less than the reference value Rref, normal operation of the internal combustion engine 1 is performed (step S24).

In this embodiment, the operating state of the internal combustion engine 1 is switched between the low load operation and the normal operation based on whether the change rate R of the electrical resistance is equal to or less than the reference value Rref. However, based on the change speed of other concentration parameters that change in accordance with the concentration of impurities contained in the water stored in the water pan 6, the operating state of the internal combustion engine 1 may be switched between the low load operation, the no-load operation, and the normal operation.

Third Embodiment

Next, the internal combustion engine 1 according to a third embodiment will be described with reference to FIG. 7 . The configurations of the internal combustion engine 1 and the vehicle 100 according to the third embodiment are basically the same as the configurations of the internal combustion engine 1 and the vehicle 100 according to the first embodiment. The following description will focus on the parts that are different from the internal combustion engine 1 and the vehicle 100 according to the first embodiment.

In the above-described first embodiment, the standby period was the period required for the sliding surfaces to slide a fixed distance. In contrast, in the third embodiment, the standby period is set as a period until the value of the resistance parameter, which changes in accordance with the magnitude of the sliding resistance between the component parts of the internal combustion engine 1, becomes equal to or less than a predetermined reference value.

Here, when a film of SiO₂ and the like is not formed on the sliding surfaces of the piston ring 22 and the cylinder liner 11, the sliding resistance between the component parts is large. On the other hand, when a film of SiO₂ and the like is formed on the sliding surfaces of the component parts, the sliding resistance between the component parts is small. Therefore, in this embodiment, when the sliding resistance between the component parts is greater than a predetermined reference resistance, it is determined that a film of SiO₂ and the like is not formed on the sliding surface, and when the sliding resistance between component parts is equal to or less than a predetermined reference resistance, it is determined that a film of SiO₂ and the like is formed on the sliding surface. This makes it possible to accurately detect the formation of a film of SiO₂ and the like on the sliding surface.

Further, in the present embodiment, the internal combustion engine 1 is controlled so that the no-load operation with no load on the internal combustion engine 1 is performed until the standby period elapses after the operation of the internal combustion engine 1 is started. Therefore, during the standby period, the internal combustion engine 1 is driven by the electric motor.

FIG. 7 is a flowchart similar to FIG. 5 showing the control routine for controlling the operation of the internal combustion engine 1. The illustrated control routine is executed by the engine ECU 40 at fixed time intervals. Steps S31, S33, and S34 in FIG. 7 are the same as steps S11, S13, and S14 in FIG. 5 , respectively, so description thereof will be omitted.

When it is determined in step S31 that it is after the operation of the internal combustion engine 1 has started, the engine ECU 40 determines whether an output W of the electric motor detected by the output sensor 42 when the internal combustion engine 1 is driven by the electric motor so as to reach a predetermined rotational speed is equal to or less than a predetermined reference value Wref (step S32). Here, the greater the sliding resistance between the inner surface of the cylinder liner 11 and the outer surface of the piston ring 22, the greater the output of the electric motor for operating the internal combustion engine 1 at a predetermined rotational speed. That is, it can be said that the output of the electric motor for operating the internal combustion engine 1 at the predetermined rotational speed is the resistance parameter that changes in accordance with the magnitude of the sliding resistance between the component parts. Therefore, when a film of SiO₂ and the like is not formed on these sliding surfaces and the sliding resistance between the sliding surfaces is large, the output of the electric motor detected by the output sensor 42 is large. On the other hand, when a film of SiO₂ and the like is formed on these sliding surfaces and the sliding resistance between the sliding surfaces is reduced, the output of the electric motor detected by the output sensor 42 is reduced. The reference value Wref at this time is, for example, a value corresponding to the reference resistance described above.

When it is determined in step S32 that the output W of the electric motor is greater than the reference value Wref, the no-load operation of the internal combustion engine 1 is operated, and the internal combustion engine 1 is driven by the electric motor (step S33). On the other hand, when it is determined in step S32 that the output W of the electric motor is equal to or less than the reference value Wref, the normal operation of the internal combustion engine 1 is performed (step S34).

In this embodiment, the operating state of the internal combustion engine 1 is switched between the no-load operation and the normal operation based on whether the output W of the electric motor is equal to or less than the reference value Wref. However, based on the other resistance parameters that change in accordance with the sliding resistance of the component parts of the internal combustion engine 1, the operation state of the internal combustion engine 1 may be switched between the low load operation or the no-load operation, and the normal operation.

Fourth Embodiment

Next, the internal combustion engine 1 according to a fourth embodiment will be described with reference to FIG. 8 . The configurations of the internal combustion engine 1 and the vehicle 100 according to the fourth embodiment are basically the same as the configurations of the internal combustion engine 1 and the vehicle 100 according to the first to third embodiments. The following description will focus on the parts that are different from the internal combustion engine 1 and the vehicle 100 according to the first to third embodiments.

FIG. 8 is a schematic cross-sectional side view of an internal combustion engine 1 according to the fourth embodiment. As shown in FIG. 8 , in this embodiment, the water supply device includes a filter 36 that removes SiC ceramics contained in the water supplied to the inner surface of the cylinder liner 11 and the outer surface of the piston ring 22, that is, the water supplied to the sliding surfaces of the component parts of the internal combustion engine 1. Specifically, in this embodiment, the filter 36 is provided in the water flow path between the strainer 31 and the pump 32.

As described above, when the sliding surfaces of the SiC ceramics slide against each other, especially when the lubrication of the sliding surfaces is insufficient, the sliding surfaces are scraped with each other and the SiC ceramic powder is mixed in the water stored in the water pan 6. When the water containing large-sized powder among such powders is supplied to the sliding surfaces, scratches may be formed on the sliding surfaces. According to the present embodiment, since large-sized SiC ceramic powder is removed in the filter 36, it is possible to suppress the formation of scratches on the sliding surfaces.

In this embodiment, the filter 36 is provided in the water flow path between the strainer 31 and the pump 32. However, if the filter 36 can be removed from the water before it is supplied to the sliding surface, the filter 36 may be provided in another flow path.

Fifth Embodiment

Next, the internal combustion engine 1 according to a fifth embodiment will be described with reference to FIGS. 9 to 11 . The configurations of the internal combustion engine 1 and the vehicle 100 according to the fifth embodiment are basically the same as the configurations of the internal combustion engine 1 and the vehicle 100 according to the first to fourth embodiments. The following description will focus on the parts that are different from the internal combustion engine 1 and the vehicle 100 according to the first to fourth embodiments.

FIG. 9 is a schematic cross-sectional side view of an internal combustion engine 1 according to the fifth embodiment. FIG. 10 is a diagram schematically showing a hardware configuration of the vehicle 100 regarding a control of the internal combustion engine 1 according to the fifth embodiment. As shown in FIGS. 9 and 10 , in this embodiment, the internal combustion engine 1 includes a stirring device 37 for stirring water stored in the water pan 6, and a stirring actuator 45 for driving the stirring device 37.

The stirring device 37 is arranged in the water pan 6 and stirs the water stored in the water pan 6 when driven by the stirring actuator 45. When the water stored in the water pan 6 is stirred, the SiC ceramic powder is uniformly dispersed in this water.

The stirring actuator 45 is connected to the stirring device 37 to drive the stirring device 37. Further, as shown in FIG. 10 , the stirring actuator 45 is connected to the engine ECU 40 via the in-vehicle network 63. Therefore, the stirring device 37 is controlled by the engine ECU 40.

By the way, as described above, when the sliding surfaces of the SiC ceramic slide against each other, the water stored in the water pan 6 is mixed with the SiC ceramic powder. Among them, when water containing fine SiC ceramic powder is supplied to the sliding surface, this SiC ceramic powder contributes to the reaction of the above formula (1) or formula (2) and the formation of SiO₂ hydrate, and as a result, SiO₂ and the like become easily formed on the sliding surfaces. Therefore, in this embodiment, the water stored in the water pan 6 is stirred by the stirring device 37 from when the operation of the internal combustion engine 1 is started until the predetermined standby period elapses. As a result, SiO₂ and the like are likely to be formed on the sliding surfaces early after the internal combustion engine 1 starts operating.

FIG. 11 is a flowchart similar to FIG. 5 showing the control routine for controlling the operation of the internal combustion engine 1. The illustrated control routine is executed by the engine ECU 40 at fixed time intervals. Steps S41 to S44 in FIG. 11 are the same as steps S11 to S14 in FIG. 5 , respectively, so description thereof will be omitted.

When it is determined in step S42 that the elapsed time T is less than the reference time Tref, the load of the internal combustion engine 1 is set to the first load L1 (step S43) and the stirring device 37 is operated (step S45). Therefore, the water stored in the water pan 6 is stirred, and the water containing the SiC ceramic powder is supplied to the sliding surfaces. On the other hand, when it is determined in step S12 that the elapsed time T is equal to or greater than the reference time Tref, the load of the internal combustion engine 1 is set to the second load L2 (step S44) and the stirring device 37 is stopped. For this reason, the water stored in the water pan 6 is not stirred and thus, the sliding surfaces are supplied with the water that does not contain much SiC ceramic powder.

In the fifth embodiment, the stirring device is stopped after the predetermined standby period has elapsed since the operation of the internal combustion engine 1 is started. Therefore, the power consumption associated with the operation of the stirring actuator 45 can be suppressed. However, the stirring device may continue to operate even after the predetermined standby period has elapsed since the operation of the internal combustion engine 1 is started.

Moreover, also in this embodiment, a filter may be provided in the water supply device similar to the fourth embodiment. In this case, the SiC ceramic powder having a large particle size is removed by the filter. Therefore, it is possible to quickly form SiO₂ and the like on the sliding surfaces while suppressing the sliding surfaces from being damaged by the supply of large SiC ceramic powder to the sliding surfaces.

Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to these embodiments, and various modifications and alterations can be made within the scope of the claims. 

What is claimed is:
 1. An internal combustion engine in which component parts slide against each other during operation, the internal combustion engine comprising: a water supply device that supplies water to sliding surfaces of the component parts; and a control device that controls an operation of the internal combustion engine, wherein at least one of the sliding surfaces of the component parts is made of silicon-based ceramics, and wherein the control device controls the operation of the internal combustion engine such that a low load or a no-load operation in which an engine load is limited to a predetermined reference load or less is performed until a predetermined standby period elapses after the operation of the internal combustion engine is started, and controls the operation of the internal combustion engine such that a normal operation in which the engine load is not limited to the reference load or less is performed after the standby period elapses.
 2. The internal combustion engine according to claim 1, wherein the standby period is a period required for a cumulative sliding distance between the sliding surfaces of the component parts to reach a predetermined fixed distance.
 3. The internal combustion engine according to claim 2, wherein the standby period is a predetermined fixed time.
 4. The internal combustion engine according to claim 1, further comprising a concentration parameter detection device that detects a value of a concentration parameter that changes in accordance with a concentration of impurities contained in water supplied to the sliding surfaces, wherein the water supply device repeatedly supplies water to the sliding surfaces, the water being water that has already been supplied to the sliding surfaces, and wherein the standby period is a period until a change speed of the value of the concentration parameter detected by the concentration parameter detection device becomes equal to or less than a predetermined reference value.
 5. The internal combustion engine according to claim 4, wherein the concentration parameter is an electrical resistance of water supplied to the sliding surfaces.
 6. The internal combustion engine according to claim 1, further comprising a resistance parameter detection device that detects a value of a resistance parameter that changes in accordance with a magnitude of a sliding resistance between the component parts, wherein the standby period is a period until the value of the resistance parameter detected by the resistance parameter detection device becomes a value indicating that the magnitude of the sliding resistance is equal to or less than a predetermined reference value.
 7. The internal combustion engine according to claim 6, wherein the internal combustion engine is configured to be driven by a motor, and wherein the resistance parameter is an output of the motor when the internal combustion engine is driven by the motor so as to reach a predetermined rotational speed.
 8. The internal combustion engine according to claim 1, wherein the water supply device includes a filter that removes powder of the silicon-based ceramics contained in water supplied to the sliding surfaces.
 9. The internal combustion engine according to claim 1, further comprising a storage portion in which water after being supplied to the sliding surfaces is stored, and a stirring device that stirs water stored in the storage portion, wherein the water supply device supplies water stored in the storage portion to the sliding surfaces, and wherein the control device causes the stirring device to stir water stored in the storage portion until the standby period elapses after the operation of the internal combustion engine is started.
 10. The internal combustion engine according to claim 1, comprising a cylinder and a piston ring that is provided on an outer circumference of a piston that reciprocates within the cylinder, as the component parts that slide against each other.
 11. The internal combustion engine according to claim 10, wherein the water supply device includes a water jet for spraying water toward the piston and a piston passage provided in the piston, and wherein the piston passage is provided such that water sprayed from the water jet flows into the piston passage and water in the piston passage is supplied to the piston ring.
 12. The internal combustion engine according to claim 1, wherein the internal combustion engine is an internal combustion engine that uses hydrogen as fuel. 